Musannaf Ibn Abi Shayba 3:3785

Jarir narrated to us, from Mansur, who said: There was a roof next to our mosque, to the right of the mosque, lower than the Imam. There were people fleeing during the governorship of al-Hajjaj, and between them and the mosque was a long wall. They would pray on that roof and follow the Imam. I mentioned this to Ibrahim, and he considered it good.